Chemical Equilibrium
I. Not all chemical reactions proceed essentially to completion. Many reactions stop at a certain point and
reach dynamic equilibrium which is when the reaction is still going but the net concentrations of reactants and
products remains constant.
A. Equilibrium Constant: By the law of mass action the concentration of products to the power of their coefficients
divided by the concentration of reactants to the power of their coefficients equals the equilibrium constant.
If the reaction is flipped then the K varies directly (i.e. K=[H2O]2/[H2]2[O2]). In addition, any change in coefficients
or direction is applied to K.
B. Heterogeneous reactions involve different phases of compounds. In the equilibrium equation liquids and solids
are neglected.
C. The reaction quotient (Q) is the constant that is acquired from the initial concentrations of the reaction
(Use the same equation as the equilibrium constant). This constant is compared to the equilibrium constant and
is then used to predict which direction the equation will shift. If the Q is smaller than K it will shift left
and vice versa.
II. Gas Constants
A. Kp is the equilibrium constant of gas pressures. K is related to Kp in the equation: Kp=K(RT)change in n.
The equation of equilibrium of gas pressure is treated the same as the equilibrium of concentrations.
III. Le Chatelier's Principle is the theory that shows concentration of species, temperature, and pressure
shifts the equation.
A. Increasing the concentration of a species will cause the equation to shift to the opposite side. Decreasing
the concentration on one side will shift the equation in the direction of that species.
B. Increasing the temperature will cause the equation to shift in the direction that consumes energy (positive
H). Decreasing the temperature causes the equation to shift in the direction that releases energy (negative H).
C. Increasing the pressure favors the side of the equation with fewer moles while decreasing the pressure favors
the side of the equation with more moles.